The announcement comes at a time of extreme uncertainty about the future of the U.S. health care system. A Republican plan to unwind key pieces of the Affordable Care Act failed in the U.S. Senate last week, but President Donald Trump has repeatedly urged lawmakers to keep working on it. Trump has threatened to end payments that insurance companies receive to keep down out-of-pocket costs for lower-income consumers.

Covered California, the state’s insurance exchange, warned earlier this year that failing to guarantee those checks, known as cost-sharing reduction payments, would lead to significant cost spikes for 2018 health plans. Insurance plans for next year will be available for purchase in California between Nov. 1 and Jan 31.

For the most popular plans, known as the “silver” tier, insurers have been asked to provide two rates — one that assumes the cost-sharing reduction payments continue and another that assumes they do not.

Covered California sells health plans to about 1.4 million people who don’t get coverage from an employer or from the two large government-funded programs, Medicare and Medi-Cal. The exchange is a central piece of Obama’s health insurance overhaul, allowing people to compare policies and collect a subsidy if they qualify based on income.

The announcement comes at a time of extreme uncertainty about the future of the U.S. health care system. A Republican plan to unwind key pieces of the Affordable Care Act failed in the U.S. Senate last week, but President Donald Trump has repeatedly urged lawmakers to keep working on it. Trump has threatened to end payments that insurance companies receive to keep down out-of-pocket costs for lower-income consumers.

Covered California, the state’s insurance exchange, warned earlier this year that failing to guarantee those checks, known as cost-sharing reduction payments, would lead to significant cost spikes for 2018 health plans. Insurance plans for next year will be available for purchase in California between Nov. 1 and Jan 31.

For the most popular plans, known as the “silver” tier, insurers have been asked to provide two rates — one that assumes the cost-sharing reduction payments continue and another that assumes they do not.

Covered California sells health plans to about 1.4 million people who don’t get coverage from an employer or from the two large government-funded programs, Medicare and Medi-Cal. The exchange is a central piece of Obama’s health insurance overhaul, allowing people to compare policies and collect a subsidy if they qualify based on income.

Trump maintains that Obama’s health law is “imploding” and must be fixed, pointing to rising costs and declining choices in the individual insurance market. A handful of rural counties around the country have been left without any insurers offering plans through Affordable Car Act marketplaces and many others have just one option.

California has seen costs rise — insurers here raised their premiums by more than 13 percent on average last year — but it’s maintained a competitive marketplace with several competing options for consumers statewide.

Costs tend to vary significantly across the state, with higher prices in Northern California where consolidation among hospitals and doctors has given them more leverage to negotiate higher payments from insurers.

Obama’s health care law provides two kinds of subsidies to help keep costs down for people with low to moderate incomes. Tax credits reduce monthly premiums for people who qualify. And payments to insurance companies cover a portion of their out-of-pocket costs, reducing the high deductibles and copays that are standard for plans in the individual market.

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This story has been corrected to show that the enrollment period for next year in California ends on Jan. 31, not Dec. 15.